1. Field of the Invention
This invention relates to an active suspension for a vehicle in which individual suspension units maintain an appropriate relationship between the roadwheels and the body of the vehicle through the use of forces generated by electric motors, with one of such motors positioned within each of the suspension units. As used herein, the terms "body" and "chassis" mean either a conventional unitized automotive body or a conventional frame and body automobile or any combination thereof.
2. Disclosure Information
For many years, vehicle suspensions, in general, and automotive suspensions, in particular, have been characterized by the use of spring elements and damping elements for controlling the motion of a vehicle body with respect to the roadwheels. Realizing, however, the inflexibility of fixed rate damping and spring element systems, designers have sought to provide a variety of adaptive control systems in which spring rates, ride heights, and/or damping rates could be varied as a result of such criteria as road inputs, vehicle turning maneuvers, vehicle loading, and other variables. U.S. Pat. Nos. 4,333,668; 4,506,909; 4,564,215; 4,635,959 and 4,673,194 all disclose unpowered or low-powered systems for varying damping rate in response to sensed vehicular operating conditions. Similarly, U.S. Pat. Nos. 4,185,845; 4,466,625; 4,568,096 and 4,630,840 all disclose systems for adjusting or maintaining vehicle ride height in response to slow changes in vehicle load.
Although adaptive suspensions have allowed increased ride control by virtue of the ability to change the damping and spring rate characteristics of the suspension, such unpowered systems are generally incapable of counteracting force inputs rising from excitation of the roadwheel and tire assembly by road surface imperfections as well as during turning, braking and acceleration maneuvers. As a result, designers sought to implement so-called active suspensions capable of responding to road inputs in real time with power inputs having sufficient robustness to control body motion. As used herein, the term "active suspension" means a suspension which has frequency response and power output characteristics sufficient to respond in real time to control force inputs to the vehicle chassis arising from such sources as road imperfections, crosswinds, and vehicle turning maneuvers.
Two examples of active suspensions are shown in U.S. Pat. Nos. 4,625,993 and 4,639,013. The '993 patent discloses a system in which the suspension units include a double acting hydraulic actuator for maintaining the location of the roadwheel and tire assembly versus the chassis of the vehicle. The '013 patent discloses a suspension unit in which a variable offset gas spring and a double acting hydraulic actuator are operated in parallel with each other. Both of these systems suffer from common shortcomings inasmuch as such hydraulically powered systems require complex piping and valve componentry. Further, in order to maintain a sufficient head of hydraulic energy for use at any given period of time, an engine driven pump must be continuously operated, thereby extracting energy from the vehicle engine which could otherwise be used to operate the vehicle, even at times when the pump output is not needed. Finally, such hydraulic systems generally are characterized by a high level of objectionable noise emissions.
It is an object of the present invention to provide an electrically powered active suspension for a vehicle in which an electrically driven assembly powered by an electric motor provides up to all of the force required for positioning a roadwheel with respect to the chassis of the vehicle.
It is an advantage of the present invention that an electrically powered active suspension according to this invention will not require the input of significant power while operating in a standby mode.
It is yet another advantage of the present invention that an electrically powered active suspension according to this invention will consume less power than a hydraulic system of comparable output because the conversion of electrical energy to mechanical energy by the suspension units described herein will be more efficient than the conversion of hydraulic energy to mechanical energy by known hydraulic active suspension systems.
It is yet another advantage of the present invention that an electrically powered active suspension according to this invention will permit regenerative operation in which mechanical energy is converted to electrical energy and returned to the electrical energy source, thereby further improving efficiency.
It is yet another advantage of the present invention that an electrically powered active suspension according to this invention will not exhibit the unfavorable noise, vibration and harshness characteristics commonly found with hydraulically powered active suspension systems.
It is yet another advantage of the present invention that an electrically powered active suspension system according to this invention will be more amenable to computer control of the suspension system, which will help to control the power load demands placed by this system upon the vehicle engine or other prime mover.
It is yet another advantage of the present invention that a system according to this invention will have lower system weight than a hydraulically powered system of similar capacity.
It is a feature of a system according to the present invention that very low system response times will permit much flexibility in tuning this system to a particular vehicle.
Other objects, features and advantages of the present invention will become apparent to the reader of this specification.